Stable lubricant emulsion

ABSTRACT

A stable lubricant emulsion composition for use in engine and gear applications is provided. The emulsion includes a base petroleum oil, an aqueous salt solution that functions as a friction/wear modifier, and a polymeric non-ionic surfactant composition having a hydrophilic-lipophilic balance value in the range of 2.5 to 7 and an average molecular weight in the range of 1,000 to 3,000. The surfactant composition may include a polyester surfactant, a PIB succinimide surfactant, a PIB amine surfactant, or a mixture thereof.

CROSS REFERENCES

This application claims the benefit of U.S. Provisional Application No. 62/535,452, filed on Jul. 21, 2017, which application is incorporated herein by reference.

FIELD OF THE INVENTION

A preferred embodiment of the invention refers to a lubricant composition comprising a stable water-in-oil emulsion and a method for formulating the composition.

BACKGROUND

In engine and gear applications, such as in combustion engines or in various types of industrial equipment, lubricants are generally required in order to reduce friction between adjacent moving surfaces, which are typically metallic surfaces, as well as to reduce wear on those surfaces of the engine or equipment. Many advancements have been made in additives to base lubricants, such as hydrocarbon-based lubricating fluids including motor oils, gear oils, or hydraulic fluids. In particular, a variety of aqueous salt solutions have been developed as additives to lubricating oils. These aqueous additives comprise metal salt solutions and may provide conversion coatings to metallic surfaces, which may have a long-lasting effectiveness in reducing friction and wear, by providing for deposition of metal ions onto those metallic surfaces. For instance, it has been demonstrated that metals such as zinc and molybdenum may be deposited as a conversion coating on an iron surface by dissolving salts of these metals in an aqueous solution and delivering the metal salts to the iron surface via a base oil lubricant.

As water does not naturally mix with oils that are typically used as base lubricants, it is generally necessary to use emulsifiers in the oil/water mixture in order to provide an effective conversion coating. Because lubricant emulsions are not typically used in engine and gear applications immediately upon manufacture of the emulsion, it is generally desirable for the emulsion to have a relatively long shelf life in order to produce a commercially viable product. However, commercially available lubricant emulsions typically do not exhibit long-term stability and may become unstable within a relatively short period of time. This may result in separation of oil and water phases in addition to precipitation of solids in the emulsion composition, which may reduce efficiency of the lubricant and may result in deposition of solids within engines or other equipment.

Accordingly, a need exists in the art for a lubricating water-in-oil emulsion for providing conversion coatings to metallic surfaces that exhibits long-term stability.

SUMMARY

In one aspect, a stable lubricant emulsion is provided. The emulsion is a stable water-in-oil emulsion comprising a base oil, an aqueous salt solution, and a high molecular weight polymeric dispersant in an amount effective to form a stable emulsion. The dispersant has a hydrophilic-lipophilic balance (HLB) value preferably in the range of 4 to 6 and has a molecular weight (MW) preferably greater than 1,000. This composition provides a water-in-oil emulsion that is homogenous and transparent with no precipitation of solids after being stored for at least six weeks at room temperature (generally about 68 to 77 degrees Fahrenheit). The present composition provides an improvement over current commercially available lubricant emulsions that are not stable over extended periods of storage before use.

The present emulsion may be formulated by adding the aqueous salt solution to the base oil and adding the dispersant/surfactant while mixing the mixture. The base oil may comprise any suitable petroleum-based lubricating oil. The aqueous salt solution comprises inorganic salts and functions as a friction modifier by depositing metal ions onto metallic contact surfaces. In a preferred embodiment, the solution comprises potassium sulfate, ammonium sulfate, zinc sulfate, boric acid, and ammonium hydroxide in an aqueous solution. In other embodiments, the solution may comprise other metal compounds such as compounds comprising molybdenum.

The dispersant, or emulsifying agent, is a polymeric non-ionic surfactant having an HLB value in the range of 2.5 to 7, and preferably in the range of 4 to 6, and an average molecular weight in the range of 1,000 to 3,000, and preferably in the range of 1,000 to 2,000. The dispersant may comprise any suitable polymeric surfactant having a molecular weight in the range of 1,000 to 3,000 and an HLB value in the range of 2.5 to 7, or any mixture of such polymeric surfactants. In a preferred embodiment, the dispersant is a polyester, a polyisobutylene (PIB) succinimide, a polyisobutylene (PIB) amine, or a mixture thereof. In another preferred embodiment, the dispersant is a mixture of dispersants comprising a polyester mixed with a PIB succinimide or with a PIB amine.

Accordingly, one object of the present disclosure is to provide a lubricant emulsion comprising a petroleum base oil, a friction modifier comprising an aqueous salt solution, and a high molecular weight polymeric dispersant having an HLB value in the range of 2.5 to 7. Another object of the present disclosure is to provide a lubricant emulsion that remains stable over an extended period of time when stored at room temperature.

DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:

FIG. 1 illustrates a reaction of polyisobutylene (PIB) succinic anhydride with diethylene triamine to produce a PIB succinimide dispersant having an average molecular weight of at least 1,000 in accordance with the present disclosure.

FIG. 2 illustrates a PIB succinimide dispersant having an average molecular weight of at least 2,000 produced by reacting PIB succinimides resulting from the reaction shown in FIG. 1 in accordance with the present disclosure.

FIG. 3 illustrates a PIB amine dispersant in accordance with the present disclosure.

DETAILED DESCRIPTION

In the Summary above and in this Detailed Description, and the claims below, and in the accompanying drawings, reference is made to particular features, including method steps, of the invention. It is to be understood that the disclosure of the invention in this specification includes all possible combinations of such particular features. For example, where a particular feature is disclosed in the context of a particular aspect or embodiment of the invention, or a particular claim, that feature can also be used, to the extent possible, in combination with/or in the context of other particular aspects of the embodiments of the invention, and in the invention generally.

The term “comprises” and grammatical equivalents thereof are used herein to mean that other components, ingredients, steps, etc. are optionally present. For example, an article “comprising” components A, B, and C can contain only components A, B, and C, or can contain not only components A, B, and C, but also one or more other components.

Where reference is made herein to a method comprising two or more defined steps, the defined steps can be carried out in any order or simultaneously (except where the context excludes that possibility), and the method can include one or more other steps which are carried out before any of the defined steps, between two of the defined steps, or after all the defined steps (except where the context excludes that possibility).

In one aspect, a stable lubricant emulsion is provided. The emulsion is a stable water-in-oil emulsion comprising a base oil, an aqueous salt solution, and a high molecular weight polymeric dispersant in an amount effective to form a stable emulsion. As used herein, the term “stable emulsion” refers to a water-in-oil micro-emulsion that remains homogenous and transparent with no observable precipitation of solids when stored at room temperature (generally about 68 to 77 degrees Fahrenheit, though room temperature may encompass a greater range, such as about 60 to 86 degrees Fahrenheit), preferably for a period of time of at least six weeks.

The base oil is preferably a composition comprising a petroleum oil or a mixture of petroleum oils. The aqueous salt solution comprises dissolved inorganic salts and functions as a friction modifier by depositing metal ions on to metallic contact surfaces. In a preferred embodiment, the solution comprises potassium sulfate, ammonium sulfate, zinc sulfate, boric acid, and ammonium hydroxide in an aqueous solution.

The dispersant, which functions as an emulsifying agent, is a polymeric non-ionic surfactant having a hydrophilic-lipophilic balance (HLB) value in the range of 2.5 to 7, and preferably in the range of 4 to 6, and having an average molecular weight in the range of 1,000 to 3,000, and preferably in the range of 1,000 to 2,000. In a preferred embodiment, the dispersant is a polyester, a polyisobutylene (PIB) succinimide, a polyisobutylene (PIB) amine, or a mixture thereof. In another preferred embodiment, the dispersant is a mixture of dispersants comprising a polyester mixed with a PIB succinimide or with a PIB amine.

HLB values were calculated using Davis' formula, of which an example calculation is the following:

HLB=7+SUM of (hydrophilic groups−n hydrophobic groups×0.475)

For instance, for oleic acid the formula is as follows:

CH3(Ch2)17COOH HLB=7+(2.1−18*0.475)=7+(2.1−8.55)=0.55

Sample emulsion compositions were prepared, and an HLB value was calculated for each sample. These HLB calculations were then used to determine the range and type of surfactants that were most effective in forming a stable water-in-oil emulsion. The interfacial tension between two immiscible phases dictates the strength of the surfactant used. Since the present emulsion comprises water and oil, the interfacial tension is large. Nonetheless, the HLB range in the solubility test included a range of surfactants having an HLB value from −24 to 55. The most effective HLB value range was determined to be from 2.5 to 7.

The present emulsion may be formulated by adding the aqueous salt solution to the base oil and adding the dispersant while mixing or stirring the mixture to form a stable micro-emulsion. Sample emulsion compositions were prepared using two different aqueous salt solutions. The first aqueous salt solution was prepared containing zinc sulfate and boric acid. This sample solution comprises 13.07 grams/liter (g/L) potassium sulfate and 43.61 g/L ammonium sulfate. The pH of the solution is adjusted to 7.0 by adding a quantity of ammonium hydroxide. Zinc sulfate heptahydrate (or alternatively anhydrous zinc sulfate) and boric acid are added to the solution, which is heated and stirred until all solids are dissolved. The pH is then adjusted to 9.0 by adding additional ammonium hydroxide. In the sample aqueous solution utilized, the final solution contained 13.07 g/L potassium sulfate, 43.61 g/L ammonium sulfate, 17.50 g/L zinc sulfate, 10.0 g/L boric acid, and approximately 26 g/L free ammonium hydroxide. This composition may be utilized to provide a conversion coating on metallic surfaces in various engine and gear applications. This composition is referred to herein as Aqueous Solution One (AS-1).

A second aqueous solution was prepared containing molybdenum hydroxide and boric acid. On a mole basis, this composition preferably comprises approximately 2.02 moles/kilogram solution (mol/kg) K⁺ (potassium ions), 0.19 mol/kg SO₄ ⁻² (sulfate ions), 1.59 mol/kg silicon, 0.155 mol/kg boron, 0.054 mol/kg molybdenum, and 2.87 mol/kg NH₃ (free ammonium hydroxide). This composition is referred to herein as Aqueous Solution Two (AS-2). This composition performs the same friction/wear modifying function as AS-1. Other aqueous salt solutions suitable for use as a friction modifier may be utilized.

Various example lubricant emulsion compositions were then prepared using one of the aqueous salt solutions AS-1 or AS-2. The aqueous salt solution was first added to a base oil, which may comprise a motor oil, a pump oil, or other suitable petroleum oil or mixture of petroleum oils. To eliminate any potential effects on stability caused by oil additives, a pump oil that contained no additives was utilized in formulating example emulsion compositions. As used herein, the term “base oil”, which includes pump oils, refers to any petroleum oil suitable for motor, gear, or pump applications, or any similar application having moving metallic contact surfaces.

A surfactant composition was subsequently added to the mixture of base oil and aqueous salt solution while stirring the composition to form a micro-emulsion. The surfactant composition may comprise a polyester, a PIB succinimide, a PIB amine, or any mixture thereof. The surfactant composition has an HLB value in the range of 2.5 to 7, and preferably in the range of 4 to 6, and an average molecular weight in the range of 1,000 to 3,000, and preferably in the range of 1,000 to 2,000. When utilizing a polyester surfactant, the hydrophilic units are preferably polyoxyalkylene units, which may be polyoxyethylene units, and the hydrophobic units are preferably long chain hydrocarbon residues. Suitable polyester surfactants of this type are available from Croda International PLC, under the trademark Hypermer, and particularly under the mark Hypermer A70.

The PIB succinimide may be produced by reacting PIB succinic anhydrides with an amine. For instance, the PIB succinimide utilized in the sample emulsion formulations herein was produced by reacting 1,000 MW PIB succinic anhydride with diethylene triamine to produce a PIB succinimide having an average MW of at least 1,000. FIG. 1 illustrates an example of this reaction. The resulting PIB succinimides may react to form a PIB succinimide having an average MW of 2,000 or greater, as shown in FIG. 2, for example. In other example formulations, the amine utilized to produce PIB succinimide may comprise other amines including, but not limited to, ethylene diamine, triethylene tetraamine, tetraethylene pentamine, and pentaethylene hexamine. Suitable PIB succinimide surfactants of this type are available from The Lubrizol Corporation.

In other formulations, the surfactant composition may comprise a PIB amine having an average MW of at least 1,000. Suitable PIB amine surfactants of this type, such as the surfactant shown in FIG. 3, are available from the company BASF SE. In a preferred embodiment, the surfactant composition is a mixture comprising a polyester mixed with a PIB succinimide or a polyester mixed with a PIB amine.

The following example formulations of a lubricant emulsion were prepared and tested for emulsion stability. All samples were prepared in duplicate using AS-1 and AS-2 in separate samples. No difference in emulsion stability was observed between AS-1 and AS-2 formulations. Examples 1-3 were prepared using Hypermer A70 polyester surfactant only. Example 4 was prepared using a PIB succinimide surfactant only. Examples 5-7 were prepared using a mixture of Hypermer A70 and PIB succinimide. The average molecular weight of each surfactant or surfactant mixture was in the range of 1,000 to 3,000.

Example 1

132.2 grams pump oil, 2 mL AS-1/AS-2, and 26.4 grams Hypermer A70 (HLB=6.8).

Example 2

133.1 grams pump oil, 2 mL AS-1/AS-2, and 40 grams Hypermer A70 (HLB=6.8).

Example 3

125 grams pump oil, 2 grams AS-1/AS-2, and 30 grams Hypermer A70 (HLB=6.8).

Example 4

125 grams pump oil, 2 grams AS-1/AS-2, and 25 grams Lubrizol PIB succinimide (HLB=3).

Example 5

125 grams pump oil, 2 grams AS-1/AS-2, 15 grams Hypermer A70, and 10 grams Lubrizol PIB succinimide (HLB=5.2).

Example 6

125 grams pump oil, 2 grams AS-1/AS-2, 30 grams Hypermer A70, and 10 grams Lubrizol PIB succinimide (HLB=5.85).

Example 7

125 grams pump oil, 2 grams AS-1/AS-2, 25 grams Hypermer A70, and 10 grams Lubrizol PIB succinimide (HLB=5.71).

Each of the above example emulsion compositions were tested for stability by storing the emulsions at a room temperature of about 70 degrees Fahrenheit for more than six weeks. After four weeks, the emulsion compositions utilizing only the polyester surfactant (Hypermer A70) or only the PIB succinimide surfactant began to separate. Examples 5-7, utilizing a mixture of polyester and PIB succinimide surfactants, resulting in an HLB value in the range of 4 to 6 for the surfactant mixture, resulted in emulsions that were stable for at least six weeks.

Additional example compositions were formulated using either a PIB amine surfactant only or a mixture of Hypermer A70 and PIB amine. Examples 8-13 were prepared using a BASF PIB amine surfactant, such as the surfactant shown in FIG. 3. Examples 14-15 were prepared using a mixture of Hypermer A70 and PIB amine surfactants. All samples were prepared in duplicate using AS-1 and AS-2 in separate samples. No difference in emulsion stability was observed between AS-1 and AS-2 formulations. The average molecular weight of each surfactant or surfactant mixture was in the range of 1,000 to 3,000.

Example 8

125.7 grams pump oil, 1 gram AS-1/AS-2, 5.4 grams BASF PIB amine (HLB=2.8).

Example 9

125.7 grams pump oil, 1 gram AS-1/AS-2, 10 grams BASF PIB amine (HLB=2.8).

Example 10

125.1 grams pump oil, 1 gram AS-1/AS-2, 15 grams BASF PIB amine (HLB=2.8).

Example 11

125.0 grams pump oil, 1 gram AS-1/AS-2, 20 grams BASF PIB amine (HLB=2.8).

Example 12

125.2 grams pump oil, 1 gram AS-1/AS-2, 25 grams BASF PIB amine (HLB=2.8).

Example 13

126.8 grams pump oil, 1 gram AS-1/AS-2, 30 grams BASF PIB amine (HLB=2.8).

Example 14

125.0 grams pump oil, 1 gram AS-1/AS-2, 5.2 grams Hypermer A70, and 20.0 grams BASF PIB amine (HLB=3.63).

Example 15

125.0 grams pump oil, 1 gram AS-1/AS-2, 10.4 grams Hypermer A70, and 16.0 grams BASF PIB amine (HLB=4.38).

Each of the above example emulsion compositions were tested for stability by storing the emulsions at a room temperature of about 70 degrees Fahrenheit for more than six weeks. Emulsion examples 8-14 experienced separation, while example 15, which had a surfactant mixture with an HLB value of 4.38, remained stable after six weeks.

Based on testing of the above sample compositions, it was determined that the most effective compositions in terms of emulsion stability are those utilizing a high molecular weight polymeric, non-ionic surfactant composition having an HLB value in the range of 2.5 to 7, and preferably in the range of 4 to 6, and an average MW in the range of 1,000 to 3,000, and preferably in the range of 1,000 to 2,000. Further, the most effective surfactant composition was a mixture of a polyester surfactant mixed with a PIB succinimide surfactant or mixed with a PIB amine surfactant, wherein the surfactant mixture had an HLB value in the range of 4 to 6. These micro-emulsion compositions exhibited no observable precipitation of solids and remained homogenous and transparent after six weeks of storage at room temperature, which provides an improvement over current commercially available lubricant emulsions that are generally not stable when stored for such a period of time.

It is understood that versions of the invention may come in different forms and embodiments. Additionally, it is understood that one of skill in the art would appreciate these various forms and embodiments as falling within the scope of the invention as disclosed herein. 

What is claimed is:
 1. A lubricant composition, said composition comprising a water-in-oil emulsion comprising: a base oil; a friction modifier in the form of an aqueous salt solution; and a polymeric dispersant in an amount effective to form a stable emulsion, wherein the dispersant has an average molecular weight in the range of 1,000 to 3,000 and a hydrophilic-lipophilic balance value in the range of 2.5 to
 7. 2. The lubricant composition of claim 1, wherein the dispersant has a hydrophilic-lipophilic balance value in the range of 4 to
 6. 3. The lubricant composition of claim 1, wherein the dispersant has an average molecular weight in the range of 1,000 to 2,000.
 4. The lubricant composition of claim 1, wherein the dispersant comprises a polyester surfactant, a PIB succinimide surfactant, a PIB amine surfactant, or a mixture thereof.
 5. The lubricant composition of claim 1, wherein the dispersant comprises a polyester surfactant mixed with a PIB succinimide surfactant.
 6. The lubricant composition of claim 1, wherein the dispersant comprises a polyester surfactant mixed with a PIB amine surfactant.
 7. The lubricant composition of claim 1, wherein the emulsion is stable for at least six weeks.
 8. A method for formulating a water-in-oil emulsion comprising: a base oil; a friction modifier in the form of an aqueous salt solution; and a polymeric dispersant having an average molecular weight in the range of 1,000 to 3,000 and having a hydrophilic-lipophilic balance value in the range of 2.5 to 7, said method comprising the steps of: adding the aqueous salt solution to the base oil; adding the dispersant to the base oil and to the aqueous salt solution to form a mixture; and mixing the mixture to form the emulsion, wherein the dispersant is added in an amount effective to form a stable emulsion.
 9. The method of claim 8, wherein the dispersant has a hydrophilic-lipophilic balance value in the range of 4 to
 6. 10. The method of claim 8, wherein the dispersant has an average molecular weight in the range of 1,000 to 2,000.
 11. The method of claim 8, wherein the dispersant comprises a polyester surfactant, a PIB succinimide surfactant, a PIB amine surfactant, or a mixture thereof.
 12. The method of claim 8, wherein the dispersant comprises a polyester surfactant mixed with a PIB succinimide surfactant.
 13. The method of claim 8, wherein the dispersant comprises a polyester surfactant mixed with a PIB amine surfactant.
 14. The method of claim 8, wherein the emulsion is stable for at least six weeks.
 15. A lubricant composition, said composition comprising a water-in-oil emulsion comprising: a base oil; a friction modifier in the form of an aqueous salt solution; and a polymeric dispersant in an amount effective to form a stable emulsion, wherein the dispersant has an average molecular weight in the range of 1,000 to 3,000 and a hydrophilic-lipophilic balance value in the range of 4 to 6, wherein the dispersant comprises a polyester surfactant mixed with a PIB succinimide surfactant or a polyester surfactant mixed with a PIB amine surfactant, and wherein the emulsion is stable for at least six weeks. 